1. Field of the Invention
The present invention relates to the field of dynamically inflated seating systems, and in particular, to such systems designed to provide periodic relief of pressure on selected body regions during seating.
2. Description of Related Art
The principle of distributing the body mass of a person over a wider surface area and reducing pressures selectively through the use of cyclically applied air pressure is well known. The seated position, for patients who can tolerate it, is often preferred by clinicians for at least part of each day. It helps to drain secretions and provides maximal lung expansion and aeration, thus helping to reduce pneumonia risk. Seated positioning also improves mental orientation in elderly patients and allows a greater participation in the activities of daily living. Unfortunately, when patients at high risk for pressure sore development are placed in seated positions for longer than about ten minutes, the chance of tissue breakdown, particularly over the ischial tuberosities, coccyx and sacrum, increases substantially.
It is known to provide some relief to the region of the ischial tuberosities with a selectively inflatable cell positioned in a pelvic recess formed in a fixed-support resilient cushion, as is disclosed in U.S. Pat. No. 4,796,948 issued to Paul et al. A similar design with left and right inflatable cells is disclosed in U.S. Pat. No. 5,022,385 issued to Harza. Both of these devices provide increased support under the ischial tuberosities without removing the support from the resilient seat cushion laterally supporting the inflatable cell(s). These designs therefore provide significant pressure variation under the ischial tuberosities, but do not significantly vary the pressures occurring on the resilient cushion, which provides for a constant amount of support.